Brake pressure control system

ABSTRACT

In a brake pressure control system provided with a discharge valve in its discharge line for the control fluid from a control chamber, the discharge valve having an on-off valve for opening and closing the discharge line so that when the discharge valve is opened, the control fluid pressure in the control chamber will be lowered to reduce directly or indirectly the braking force on the vehicle, the present invention provides a system having a second discharge valve arranged in series in the discharge line. With this system, even if one of the valves should fail to close the discharge line, the other valve will act to prevent the leakage of the control fluid pressure in the control chamber.

FIELD OF TECHNOLOGY

The present invention relates to a failsafe, highly reliable brakepressure control system for use with a vehicle having two brake pipinglines and which provides various types of brake force control includingboost control of braking force, control of distribution of brakingforce, antilock control, traction control for the wheels, and automaticbraking for maintaining the stopped state, adjusting the distancebetween the cars, and avoiding obstacles on the road.

TECHNOLOGICAL BACKGROUND

The abovementioned various types of controls of braking force haveheretofore been dealt individually by means of separate control units orseparate systems each including an electronic control unit. However,such controls are possible by combining the increase, decrease andretaining of the brake fluid pressure both in braking and non-brakingconditions. If one individual unit or system is allocated to eachcontrol factor, similar control elements have to be used for differentcontrols, thus incurring such problems as economical loss, poorreliability, reduction in the space available in the vehicle andincrease in the overall weight of the vehicle. An integrated systemwhich can comprehensively deal all the controls would be very desirable.

In U.S. Pat. No. 3,667,813, there is disclosed a system which solves theabovesaid problem in the simplest way. In this system, a shut-off valveis provided in a piping line connecting a master cylinder with a wheelbrake so as to open and close the brake fluid feed line. Also, betweenthe shut-off valve and the brake are provided an access valve whichelectromagnetically changes over to selectively introduce or hold thepump pressure produced by a pump provided separately from the mastercylinder and an electromagnetic discharge valve for selectivelydischarging or holding the fluid pressure so as to apply a pump pressureto the brakes and achieve a desired braking force. Besides, many similarsystems are known in which an electromagnetic discharge valve isprovided directly in a brake piping line. Also known are systems adaptedto control the brake force indirectly by controlling the pressure in acontrol system.

In contrast, in a system in which a discharge valve is directlyconnected to a brake line, the malfunction of the discharge valve owingto worn sealing surfaces or foreign matters mixed in the brake fluidwill directly lead to the loss of pressure on the brakes, thus bringingabout a grave danger.

Many of the systems having a control line separate from the brake lineare provided with various failsafe mechanisms so that the brake linewill supply brake pressure even in case of the failure of a dischargevalve disposed in the control line. But these systems have theirdrawbacks in that they structurally consume more brake fluid for thebrake line and that the maximum attainable brake pressure isinsufficient.

An object of the present invention is to solve the grave and criticalproblems of the prior art.

DISCLOSURE OF INVENTION

In order to achieve this object, the present invention provides a brakepressure control system including a discharge valve provided in adischarge line for control fluid fed from a control chamber and havingan on-off valve means for opening and closing the discharge line, theopening lowering the control fluid pressure in the control chamber toreduce the braking force directly or indirectly, characterized in thattwo or more valve means of the discharge valves are provided in seriesin the discharge line.

Thus, even if any one of the valves should lose its sealing function forsome reason, the remaining normal valve will prevent the leakage of thecontrol fluid from the control chamber, thus avoiding the abovesaidproblems.

The system of the present invention provides an economical arrangementand yet improves the safety of the vehicle equipped with the system. Thesafety of the system is further improved by designing the second valveto stop it from opening by utilizing an increase in the valve-closingforce by the fluid pressure in case of a failure of the first valve.

The present invention is applicable both to a system in which valves ofvarious types, important elements of the present invention, are directlyprovided in a brake piping line or in a system adapted to indirectlycontrol the brake force by controlling the pressure in a controlchamber. In other words, the same effects can be achieved in an indirectcontrol system and various failsafe mechanisms used in the prior artsystem are not required any more.

The term "control chamber" herein used refers to the area where thecontrol fluid from the pressure source is present.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are circuit diagrams of embodiments of brake systems of thepresent invention with the electromagnetic valves shown in section; and

FIG. 5 is a circuit diagram of the entire system according to thepresent invention.

BEST MODE FOR EMBODYING THE INVENTION

In the system of the first embodiment shown in FIG. 1, when a brakepedal 1 is stamped down, a brake fluid pressure will be produced in amaster cylinder 2 and be transmitted to a wheel brake 4 through anormally open electromagnetic shut-off valve 3. As a second fluidpressure source for the system, there is provided a pump 7 driven by anelectric motor 5 to suck and pressurize brake fluid from a reservoirtank 6 for the master cylinder 2. The brake fluid pressurized by thepump 7 is stored in a pressure accumulator 8 and flows through anormally closed electromagnetic access valve 9, past a junction point 12between a line 10 for the pressurized fluid from the master cylinder anda pump pressure feed line 11, and through a line 13 to the brake. To thejunction point 12 is connected a discharge line 14 leading to thereservoir tank 6. Two electromagnetic discharge valves 15 and 16 of anormally closed type are provided in series in the discharge line 14.

The discharge valve 15 comprises an iron core 15b, an electromagneticcoil 15a wound around the core, a movable valve body 15c adapted to beattracted to the iron core 15b to open the discharge line 14, and aspring 15e normally biasing the valve body 15c to the valve-closingposition. The discharge valve 16 and the access valve 9 are of the sameconstruction as the valve 15.

With the system of this embodiment, when the shut-off valve 3 and theaccess valve 9 are energized and the discharge valves 15 and 16deenergized, the lines 10 and 14 are closed while the line 11 is opened.In this state, the brake fluid pressurized by the pump 7 and stored inthe pressure accumulator 8 flows into the line 13 to apply fluidpressure to the wheel brake 4. If the access valve 9 is deactivated andthe discharge valves 15 and 16 activated to close the line 11 and openthe line 14, the brake fluid in the line 13 will be discharged throughthe line 14 to lower the pressure on the wheel brake 4. If the accessvalve 9 and the discharge valves 15 and 16 are deactivated, the pressureon the wheel brake 4 will be maintained at a constant level.

Thus with this system, a desired fluid pressure can be applied to thebrake, regardless of whether the master cylinder is producing pressureor not, by controlling the access valve 9 and the discharge valves 15and 16 while keeping the line 10 closed by means of the shut-off valve3. The timing of activating and deactivating each valve can bedetermined on the basis of information supplied from sensors. The systemof the present invention thus provides an integrated control of thebraking forces which includes an antilock control, traction control forthe driving wheels, control for keeping the vehicle stopped, boostercontrol, control of the distribution of braking force, and control forthe adjustment of the distance between the cars or for avoidingobstacles on the road.

Since in the discharge line 14 two on-off valve means are provided inseries each comprising a movable valve body 15c adapted to abut a valveseat, even if one of the two valves should fail to function, the othervalve will surely shut off the discharge line, thereby ensuring areliable control of the braking force. Even in case the fluid pressuregenerated in the master cylinder 2 is applied directly to the brakeowing to the failure of the second fluid pressure source, the driverwill feel an unchanged braking effect as if both the master cylinder andthe pump circuit were normally working.

FIG. 2 shows a second embodiment of the present invention which isdifferent from the first embodiment in that a 3-port 2-positionelectromagnetic changeover valve 19 is provided in the lines 10 and 11in order to selectively supply either the pressurized fluid in themaster cylinder or the fluid from the pump circuit to a line 17, and inthat the line 17 leading to the shut-off valve 3 is branched at ajunction point 18 to another wheel brake, and in that a discharge valve25 having two on-off valve means is provided in the discharge line 14.

In this embodiment, pressure is applied to the wheel brake 4 byenergizing only the changeover valve 19 and the pressure in the line 13can be kept constant by energizing the shut-off valve 3. The system ofthe second embodiment can be more advantageously used when it isnecessary to control the pressures on two brakes independently. With thesystem of the first embodiment, two shut-off valves, two access valvesand two pairs of discharge valves, a total of eight valves are neededsince any line to another brake is branched from a junction pointprovided on the line 10. With the system of the second embodiment, sincethe line is branched after either the fluid from the master cylinder orthe fluid from the pump circuit has been selected by the changeovervalve 19, only one changeover valve is needed instead of two accessvalves as in the first embodiment. Further only one discharge valve 25will suffice for the system since it contains two on-off valves. Thus, atotal of five valves are needed for the system of the second embodiment.

The discharge valve 25 comprises an iron core 25b, an electromagneticcoil 25a wound around the core 25b, a movable valve body 25c adapted tobe attracted to the iron core 25b to open the discharge line 14, aspring 25e for biasing the valve body 25c to the valve-opening position,a rod member 25g extending through a passage 25f formed in the iron core25b, a second movable valve body 25i provided at the other end of theiron core 25b, and a spring 25h for normally biasing the second valvebody 25i in the same direction as the valve body 25c so as to close thepassage 25f. When the valve body 25c is attracted to the iron core 25bto open the discharge line 14, it pushes down the rod member 25g, thusforcing the second movable valve body 25i away from the iron core 25b toopen the passage 25f forming a part of the discharge line. Thus, thepressure in the line 13 is controlled in the same manner as in the firstembodiment. Even if one of the movable valve bodies 25c and 25i shouldlose its sealing function, the other will surely close the dischargeline to prevent the leakage of pressure.

The system of the third embodiment shown in FIG. 3 is substantially thesame as the second embodiment with the exception that there is provideda second reservoir tank 6' in communication with the reservoir tank 6and connected to an intake port of the pump 7 and the outlet of thedischarge line 14 and that the discharge valve 35 provided in thedischarge line 14 is somewhat different in construction from thedischarge valve 25 in the second embodiment. By providing the secondtank 6' separately from the master cylinder, a sufficient amount offluid will be available for circulation in the control chamber even ifthe vehicle cannot afford enough space for the capacity of the firsttank 6. Further, the discharge valve 35 has a simpler structure so thatit can be manufactured easily and can be used more safely.

The discharge valve 35 comprises an electromagnetic coil 35a andprovided with a passage 35f, an iron core 35b energized by the coil 35a,movable valve bodies 35c, 35i provided at both ends of the core 35b,which core 35b is provided with a passage 35f, and springs 35e and 35hfor biasing the respective movable valve bodies 35c, 35i away from thecore 35b to close the valve 35 (the valve body 35c is biased against theflow of the brake fluid and the valve body 35i is biased in thedirection of flow). The discharge valve 35 is different from thedischarge valve 25 of the second embodiment shown in FIG. 2 in that notonly the movable valve body 35c but also the valve body 35i areattracted to the magnetized core 35b to open the valve.

With the discharge valve 35, the brake fluid pressure acts only on thefirst on-off valve means, that is, the movable valve body 35c but not onthe second on-off valve means, that is, the movable valve body 35i.Thus, if the valve body 35c is working normally to close up thedischarge line 14 perfectly, the valve body 35i can be attracted to thecore by a small electromagnetic force which is barely enough to overcomethe bias of the spring 35h. But if the valve body 35c should lose itssealing capability, the pressure of the brake fluid will act on thevalve body 35i, increasing the valve-closing force. In this case, theelectromagnetic force required to bring the valve body 35i into thevalve-opening position is more than the sum of the bias of the spring35h and the closing pressure of the brake fluid on the valve body 35i.But for safety's sake, the electromagnetic force should be set so as tosatisfy the following formula (wherein f1 is the electromagnetic force,f2 the bias of the spring 35h, and f3 the closing pressure of the brakefluid on the valve body 35i)

    f2<f1<f2+f3                                                (1)

If f1>f2+f3, the failure of sealing by the valve body 35c cannot bedetected as long as the valve body 35i is normally performing to closethe discharge line, compensating for the failure of the valve body 35c.In contrast, if the forces are set to satisfy the formula (1), theelectromagnetic force generated by energizing the coil 35a is not strongenough to move the valve body 35i and open the discharge line 14. Thusthe failure of the valve body 35c will be detected and a warninggenerated directly from the abnormal state of pressure in the line 13 orindirectly from the abnormal rotation of the wheels which results fromthe failure of the valve body 35i. The other functions and effect of thethird embodiment are substantially the same as in the first and secondembodiments.

FIG. 4 shows a fourth embodiment which is similar to the firstembodiment in that a shut-off valve is provided between the mastercylinder 2 and the brake 4, that the same access valve 9 is provided inthe line 11 extending from the pump 7 to the junction point 12 and thatthe discharge valve 15 and a second discharge valve are provided in thedischarge line 14, but is different therefrom in that the shut-off valveand the second discharge valve are incorporated into one electromagneticvalve 20 so as to work with each other.

The electromagnetic valve 20 comprises an iron core 20b, anelectromagnetic coil 20a wound around the core, a movable valve body 20cadapted to be attracted to the core 20b to cut off the flow through apassage 20f formed between the lines 10 and 13, a spring 20e normallybiasing the valve body 20c away from the core to open the passage 20f, asecond movable valve body 20i disposed at the other end of the core 20b,and a spring 20h biasing the valve body 20i away from the core to closea passage 20k in communication with the discharge line 14 through apassage 20j. When the coil 20a is not energized, the valve bodies 20cand 20i are in the positions as shown in FIG. 4, communicating the line10 with the line 13 while cutting off the fluid flow through thedischarge line 14 leading to the tank 6' in cooperation with theshut-off valve 15.

Upon start of the brake pressure control, it is necessary to energizethe electromagnetic coil 20a to bring the shut-off valve comprising thevalve body 20c and its valve seat on the iron core 20b to thevalve-closing position in order to cut off the communication between themaster cylinder 2 and the brake 4. Simultaneously with the excitation ofthe coil 20a, the valve body 20i which constitutes the second dischargevalve is attracted to the core 20b to open the passage 20k. Theelectromagnetic force generated by the excitation of the coil 20a andother forces should satisfy the formula (1) shown in the description ofthe third embodiment so that if the discharge valve 15 should fail tocut off the discharge line 14, the valve body 20i will remain in thevalve-closing position under the brake fluid pressure even if the coil20a is energized. It is also preferable to provide a device whichdetects an abnormal condition of the pressure in the line 13 or thespeed of rotation of the wheel and gives a warning of the failure of thefirst valve. The tank 6' is provided as in the third embodiment but itneed not be provided in this embodiment.

FIG. 5 shows the fifth embodiment in which the brake pressure controlsystem is applied to a diagonal split piping. The brake fluids inseparate chambers of a tandem master cylinder 2', pressurized bystamping down the brake pedal 1, flow out through lines 10 and 10' andthrough 3-port 2-position electromagnetic changeover valves 19 and 19'so that each of the fluid flows will be divided at points 18 and 18'into two branches, i.e. the flow toward a front wheel and the flowtoward a rear wheel. The flows toward the front wheels are fed to frontbrakes 4F and 4F' through normally open shut-off valves 3F and 3F',respectively. The flows toward the rear wheels are fed to rear brakes 4Rand 4R' through normally open shut-off valves 3R and 3R', respectively.

The changeover valves 19 and 19' are provided in each of the twoindependent pipe lines so as to selectively supply either the fluid fromthe pump 7 or the fluid from the master cylinder 2' into the linesleading to the brakes. The pump pressure is generated by the pump 7,stored in the pressure accumulator 8, and kept constant by turning onand off the motor 5 for the pump 7 by means of a pressure switch 21.Discharge lines 14 branch from lines 13 connecting the shut-off valves3F, 3F', 3R and 3R' for the brakes and lead to the reservoir tank 6.Normally closed first discharge valves 15F, 15F', 15R and 15R' areprovided along the discharge lines. The brake fluid flows dischargedthrough the discharge valves are joined together at a junction point 22to return to the reservoir tank 6 through a second discharge valve 16 ofa normally closed type.

If the second discharge valve 16 is adapted to work synchronously withany of the first discharge valves 15F, 15F', 15R and 15R', the systemwill work as though there was no second discharge valve 16 when thefirst discharge valves function normally. If any of the first dischargevalves should lose their sealing function, the discharge valve 16 servesto prevent the brake pressure in the control line from falling.

Further, by setting the electromagnetic force of the second dischargevalve at such a value as to allow its movable valve body to be attractedto the valve-opening position only when the fluid pressure is not actingon the valve body as a valve-closing force, the failure of any of thefirst discharge valves will be detected since at that time the seconddischarge valve stops functioning to open the valve.

In FIG. 5 showing the fifth embodiment, the reference characters F and Rattached to numerals 3, 4 and 15 are used to designate the front wheelline and the rear wheel line, respectively. The primed and unprimednumerals are used to distinguish the right side wheels from the leftside ones.

We claim:
 1. A brake pressure control system comprising:a hydraulicwheel brake; a control chamber containing hydraulic fluid andcommunicating with said hydraulic wheel brake to supply hydraulicbraking fluid thereto; a discharge line extending from said controlchamber; at least two normally closed discharge valves connected inseries in said discharge line, and electromagnetic means operativelyassociated with said discharge valves for controlling the opening andclosing thereof in response to antilock control, traction control andthe like for the brake pressure control system to control the dischargeof hydraulic fluid from said control chamber, the downstream one of saiddischarge valves being operable to remain closed when the upstream oneof said discharge valves fails.
 2. A brake pressure control system asclaimed in claim 1 further comprising a single valve housing having saidtwo discharge valves therein, a fixed iron core in said housing, saidupstream one of said discharge valves having a valve member attractableby said iron core to be moved to the open position when said core isenergized in response to the desired control, the downstream one of saiddischarge valves having a valve member which is mechanically linked tosaid the upstream one of said discharge valves for being moved to theopen position when the valve member of said upsteam discharge valve isopened and further having means for closing the valve member of saiddownstream discharge valve when the valve member of said upstreamdischarge valve is closed and for holding said valve member of saiddownstream discharge valve closed when said upstream discharge valvemember fails.
 3. A brake pressure control system as claimed in claim 1further comprising a single valve housing having said two dischargevalves therein, a fixed iron core in said housing, said discharge valveseach having a valve member attractable by said iron core to be moved tothe open position when said core is energized in response to the desiredcontrol, and further having means for closing the valve member of saiddownstream discharge valve when the iron core is deenergized for holdingsaid valve member of said downstream discharge valve closed when saidupstream discharge member fails.
 4. A brake pressure control system asclaimed in claim 3 in which said valve member of said downstreamdischarge valve is closable in the direction of flow of hydraulic fluidthrough said discharge valves.
 5. A brake pressure control system asclaimed in claim 4 in which said means for closing the valve member ofsaid downstream discharge valve is a spring means, and said iron corehaving an attractive force for attracting said valve member of thedownstream discharge valve with a force which is smaller than the sum ofthe fluid pressure prior to the energization of said iron core and thebias force of said spring, and which is greater than the bias force ofsaid spring along.
 6. A brake pressure control system as claimed inclaim 1 further comprising a first valve housing containing saidupstream discharge valve, and a further valve housing containing saiddownstream discharge valve and a fluid pressure control valve separatefrom said downstream discharge valve for controlling fluid pressure insaid brake pressure control system upstream of said control chamber,said further valve housing having electromagnetic means forsimultaneously controlling both said downstream discharge valve and saidfluid pressure control valve for opening said valves when saidelectromagnetic means is energized.
 7. A brake pressure control systemas claimed in claim 6 in which said downstream discharge valve has avalve body movable in the closing direction in the same direction as theflow of fluid in said discharge line, and spring means biasing saidvalve body in the closing direction of said discharge valve, and saidelectromagnetic means has an attractive force exerted on said valve bodyin the opening direction of said downstream discharge valve which issmaller than the sum of the fluid pressure prior to the energization ofsaid electromagnetic means and the bias force of said spring means andwhich is greater than the bias force of said spring means alone.
 8. Abrake pressure control system as claimed in claim 6 or 7 in which saidfluid pressure control valve is an input valve for controlling the rateof flow of pressurized fluid into said control chamber.